I like options 1, 4
1 is cheapest
1,4 are retraceable-- ie you go back to stock platform without risk.
One other option, not mentioned is to buy a complete used Glock upper and start from there-- thus = or < the same price as the Brownell slide, complete with internals with barrel, then the above also still applies. If not likey, the upper with the option (x) for RMR will still garner a higher resale price.